[TC-4078]: make ListSection methods run on UI thread as required

Prior to this fix I was seeing an occasional error message in my app: java.lang.IllegalStateException: "The content of the adapter has changed but ListView did not receive a notification. Make sure the content of your adapter is not modified from a background thread, but only from the UI thread. [in ListView(-1, class android.widget.ListView) with Adapter(class android.widget.HeaderViewListAdapter)]

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